1. Field of the Disclosure
The present invention relates to non-destructive testing and inspection systems (NDT/NDI), particularly to a system operable for and a method of conducting phased array probes refraction angle verification using standard calibration blocks, including IIW blocks.
2. Related Art
Acoustic phased array (also known as “PA”) instruments provide effective inspection to detect flaws in many kinds of test objects, such as welded steel structures. It is widely known that PA instruments produce accurate, detailed cross-sectional pictures of internal structures at fast inspection speeds. Phased array technology uses multiple acoustic elements and electronic time delays to create beams that can be steered, scanned, swept, and focused electronically for fast inspection and multiple angle inspections.
A PA system is programmed to steer sound beams in a wedge medium and then, being governed by the Snell law, the sound beams propagate through the wedge-test piece interface to form sound beams at inspection angles in the test piece. These inspection angles are called “refraction angles”. Due to the complexity of the procedure, the refraction angles generated by a PA system are usually not verified or checked during existing inspection operations, despite the well-known fact that the Snell law can overestimate the refraction angles at high angles of shear waves, as is illustrated in a publication in the figure 4.29b in Section 4.6 of Ultrasonic Testing of Materials, 4th Edition published by Springer-Verlag, 1990.
In existing practice, to conduct a typical angular scan, the user usually relies heavily on the initial values of refraction angles calculated by the focal law calculator integrated in the PA instrument. A very common practice is that, without checking the refraction angles, the user conducts the ‘Wedge Delay Calibration’ with a reference reflector of known depth or known sound path in a calibration block. This procedure, by simply adjusting the beam delays in wedge, compensates for any discrepancy in the actual measurement of the known depth or known sound path. However, the discrepancy may not be induced by the wedge delays. Instead, it maybe induced by other inaccurate parameters such as the velocity in wedge, velocity in the test material, the geometrical inaccuracy of the wedge or even the inaccuracy in the electronic firing/reception. Consequently, using only the beam delays in wedge to compensate the discrepancy is not completely reliable.
The use of the function ‘wedge delay calibration’ cannot modify or update the refraction angles, but only provide compensation to correct the displayed depth or sound path to the known depth or known sound path based on the reference flaw. The refraction angle is left without any calibration in this existing practice. If the displayed refraction angle is not what the true refraction angle is, the PA instrument may induce errors elsewhere, such as the horizontally measured distance between the measured flaw and the front of the wedge would be nearer or farther than that of the true values.
In another existing practice, some phased array system users check refraction angles by following a procedure similar to the single element ultrasound (UT) refraction angle check. The procedure is detailed in ANSI Standard by American Welding Society, “AWS D1.1/D1.1M: 2006”, more particularly in Calibration of the UT Unit with IIW Block, in sections 6.29.2 Shear Wave Mode (Transverse) on Index Point and Angle and the associated figures 6.22 and 6.26. The procedure is herein referred as “ANSI Calibration” procedure which is herein incorporated by reference by the present application.
The above cited procedure of refraction angle check is not practical for phased array operation for multiple reasons, some of which are listed as follows.
Due to the involvement of many different beam angles, it is difficult to physically mark the beam exit point for each beam on the side of the PA search unit.
Due to the nature of the manual operation, the accuracy of the angle verification using the above ANSI Calibration is not desirable.
More existing effort in providing PA beam refraction angle check is disclosed by U.S. Pat. No. 6,938,457B2. The principle of the disclosed measurement procedure is guided by the manual ANSI Calibration method described above. The probe index point, according to this patent, still needs to be physically marked and the refraction angle (i.e.: the so-called induced angle in the patent) is measured with a series of scribed angle lines extended from a side-drilled hole.
It is obvious that the above ANSI Calibration operation is time consuming since the user needs to manually write down the angle values and, if necessary, to manually input the values into the PA instrument for further processing.
Thus, given the drawbacks and problems that existing methods of conducting beam angle checks, there is a need to provide a phased array angle beam check method that can be efficiently and conveniently conducted with high accuracy.